Abrasive material

ABSTRACT

A polishing material is provided in which the dispersibility of the abrasive grains of the polishing material having, as a major component, rare earth oxides including cerium oxide is made better and the hardness of abrasive grain precipitates is reduced, and at the same time high efficiency of polishing can be achieved stably. According to the present invention, in a polishing material having, as the major component, rare earth oxides including cerium oxide, any one of crystalline cellulose, calcium secondary phosphate, a condensate of sodium β-naphthalenesulphonate and formalin, and synthetic silica is contained as an anti-solidification agent capable of softening abrasive grain precipitates of the polishing material when the abrasive grains of the polishing material are dispersed into a dispersion medium, and sodium hexametaphosphate or pyrophosphate is contained as a dispersant capable of dispersing the abrasive grains of the polishing material into the dispersion medium.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a national stage filing under 35 U.S.C. §371of PCT/JP01/08671 filed on Oct. 2, 2001, and designating the U.S.

TECHNICAL FIELD

The present invention relates to a polishing material, and particularlyto additives contained in constituting a polishing material having, as amajor component, rare earth oxides including cerium oxide, composingsuch a polishing material.

BACKGROUND ART

Recently, glass materials are widely utilized, and used in numerousareas such as not only optical lens applications, but also optical andmagnetic disc applications, color filters for liquid crystals, LSIphotomasks, and others. Glass; materials for these applications requirethe smoothness of the surface with strictly high accuracy, and thereforepolishing materials having, as the major component, rare earth oxidesincluding cerium oxide have been conventionally employed for processingtheir surface.

These polishing materials having, as the major component, rare earthoxides including cerium oxide are generally used in a slurry state, inwhich the abrasive grains of a polishing material are dispersed into adispersion medium such as water. When a polishing material in thisslurry condition is allowed to stand, the dispersoid, abrasive grains ofthe polishing material, is easily separated from the dispersion medium,causing a phenomenon of precipitation.

In addition, polishing materials are used with cycling, so that theabrasive grains themselves will be ground and a glass component of asubstrate to be polished will be included, and when the abrasive grainsare precipitated, the precipitates tend to become very hard.

Such separation and precipitation of the abrasive grains will disablethe composition of a slurry having a given concentration or theconcentration from being maintained while use with cycling, therebydecreasing the efficiency of polishing. When the abrasive grainprecipitates become hard, the abrasive grains tend to readily adhereonto the glass surface of a substrate to be polished, and operations arerequired for removing the abrasive grains from the glass surface;so-called washing property on the glass surface will be thus impaired.Furthermore, the hardening of the abrasive grain precipitates tends toresult in a clogged polishing pad, which will be also a cause of formingscratches on the surface of a substrate to be polished.

Under the present condition, the above described problems in polishingglass materials are also pointed out for chemical mechanical polishing(CMP) conducted in a semiconductor manufacturing process.

In order to solve the problems of abrasive grain precipitates in apolishing slurry as described above, many proposals have beenconventionally made for additives contained in constituting a polishingmaterial.

For example, as additives for preventing abrasive grain precipitatesfrom hardening, there have been proposed ammonium phosphate salt(Japanese Patent Application Laid-Open No. 56-147880) and phosphatesalts of rare earth metals (Japanese Patent Application Laid-Open No.56-45975), magnesium chloride (Japanese Patent Application Laid-Open No.3-14658:5), calcium compounds (Japanese Patent Application Laid-Open No.6-330025), amino acids and amines (Japanese Patent Application Laid-OpenNo. 10-183104).

These additives for polishing materials are effective in terms ofredressing the hardness of the abrasive grain precipitates, but notsufficiently satisfactory in terms of the dispersibility of the abrasivegrains in a dispersion medium and the accompanying efficiency ofpolishing. Accordingly, further improvement is needed in the presentcircumstances.

DISCLOSURE OF THE INVENTION

Therefore, the present invention aims at providing a polishing materialcapable of not only improving dispersibility of abrasive grains of thepolishing material and reducing hardness of abrasive grain precipitates,but also stably achieving high efficiency of polishing.

In order to solve the above-mentioned problems, the inventors haveinvestigated additives for polishing materials, and have found that awell-balanced polishing material as a whole with respect tocharacteristics required as a polishing material is formed by containingtwo additives, an anti-solidification agent capable of softeningabrasive grain precipitates of a polishing material when abrasive grainsof the polishing material are dispersed into a dispersion medium and adispersant capable of dispersing abrasive grains of a polishing materialinto a dispersion medium, in a polishing material having, as a majorcomponent, rare earth oxides including cerium oxide.

The present invention is characterized by containing simultaneously twoadditives, an anti-solidification agent and a dispersant, inconstituting a polishing material having, as a major component, rareearth oxides including cerium oxide. According to the present invention,when abrasive grains of a polishing material are dispersed into adispersion medium, the hardening of abrasive grain precipitates of thepolishing material is not caused and the dispersibility of the abrasivegrains in the dispersion medium becomes better, and high efficiency ofpolishing can be stably maintained as a result. The polishing materialaccording to the present invention can be widely applied forsemiconductors and glass material and is especially effective as apolishing material for glass materials.

Conventionally known anti-solidification agents can be employed in thepresent invention, however the present inventors' research revealed itis preferable to employ one selected from the group consisting ofcellulose and cellulose derivatives, silicas, alginic acid and alginicacid derivatives, aromatic sulfonate formalin condensate salts, andcalcium-containing compounds.

The cellulose and cellulose derivatives as anti-solidification agentsinclude cellulose, crystalline cellulose, methylcellulose,ethylcellulose, hydroxyethylcellulose, carboxymethylcellulose,carboxymethylcellulose ammonium, alkaline metal salts and alkaline earthmetal salts of carboxymethylcellulose.

The silicas as anti-solidification agents include synthetic silica,colloidal silica, fumed silica. The alginic acid and alginic acidderivatives include sodium alginate, propylene glycol ester of alginicacid. The aromatic sulfonate formalin condensate salts include sodiumβ-naphthalene sulfonate formalin condensate. In addition, thecalcium-containing compounds include calcium sulfate, calcium hydroxide,calcium secondary phosphate.

In addition, the following substances can provide the effect similar tothat obtained by the above described anti-solidification agents.

Proteins and polypeptides (for example, glue, gelatins, albumin, casein)and starch and starch derivatives (for example, heat-treated oralkaline-treated potato starch and cornstarch, carboxymethyl starch,dimethylamino starch) can be employed. In addition, iron salts (forexample, ferric sulfate, ferrous sulfate, ferric chloride, ferrouschloride) and aluminum compounds (for example, aluminum sulfate,polyaluminum chloride, sodium aluminate) can also be employed. Organichigh-molecular flocculants can also be employed as anti-solidificationagents of the present invention. For example, polyacrylamide,poly(acrylamide/acrylate) copolymer, polyethyleneimine,polyvinylbenzyltrimethylammonium chloride, polymethacrylateN,N-diemethylaminoethyl ester salts, methacrylateN,N-diemethylaminoethyl ester salt/acrylamide copolymer,polymethacrylate trimethylammonioethyl ester salts, polymethacrylatetrimethylammonioethyl ester salt/acrylamide copolymer,N,N-dimethylaminomethylene acrylamide/acrylamide copolymer,polydiallyldimethylammonium chloride, diallyldimethylammoniumchloride/acrylamide copolymer, 2-vinylimidazoline polymer sulfate,vinylpyridine copolymer salts, dicyandiamide-formaldehyde polycondensatesalts can be mentioned. In addition, hydrogencarbonates, ligninsulfonate, polyvinyl alcohol, water-born urethane resin, gum arabic, andchitosan can be employed.

According to the research by the present inventors, it is morepreferable to use any one of crystalline cellulose, calcium secondaryphosphate, and sodium β-naphthalene sulfonate formalin condensate amongthe above described anti-solidification agents of the present invention.

Crystalline cellulose herein is a fine powder obtained by selectingrefined pulp with particularly high purity, hydrolyzing it with amineral acid under predetermined conditions, and then washing andremoving noncrystalline regions formed by the cellulose molecule,followed by grinding, purifying and drying. The inventors have foundthat when this crystalline cellulose as an anti-solidification agent isadded to a polishing material having, as the major component, rare earthoxides including cerium oxide, aggregation between the abrasive grainsof a polishing material is reduced, and the abrasive grains can beprecipitated in a relatively soft condition, whereby the hardening ofthe abrasive grain precipitates is efficiently prevented.

According to the research by the inventors, furthermore, it has turnedout that each of calcium secondary phosphate, a condensate of sodiumβ-naphthalenesulphonate and formal in, and synthetic silica also servesas an anti-solidification agent having an effect similar to that ofcrystalline cellulose. Synthetic silica for use in the present inventionmeans water-containing amorphous silicon dioxide synthesized by wetprocesses, and has a very high porosity due to possessing of a networkstructure in which minute spherical particles are chemically linked inthree dimensions.

When these anti-solidification agents are added, the hardening ofabrasive grain precipitates is effectively prevented, washing propertyis improved, the clogging of a polishing pad is suppressed, and theoccurrence of scratches on the surface of a substrate to be polished isreduced to a great extent. However, in case of containing theseanti-solidification agents alone in a polishing material, although thehardening of abrasive grain precipitates will be prevented, there is atendency to reduce the dispersibility of the abrasive grains in adispersion medium, and the efficiency of polishing is decreased. In thepresent invention, therefore, in order to suppress a decrease in theefficiency of polishing, a dispersant is added at the same time.

Although so-called surfactants that activate the surface of abrasivegrains can be employed as a dispersant in the present invention,according to the research by the inventors, it is preferable to employone selected from the group consisting of condensed phosphoric acid andcondensed phosphates, polystyrene sulfonate salts, polycarboxylate typehigh-molecular compounds, polyoxyethylene sorbitan fatty acid esters,and polyoxyethylene sorbitol fatty acid esters.

The condensed phosphoric acid and condensed phosphates includepyrophosphoric acid, sodium pyrophosphate, sodium tripolyphosphate,sodium hexametaphosphate, and the like. The polystyrene sulfonate saltsinclude sodium polystyrene sulfonate. The polycarboxylate typehigh-molecular compounds include polyacrylic acid, polymaleic acid,acrylic acid/maleic acid copolymer, polyacrylate salts, polymaleatesalts, acrylic acid/maleic acid copolymer salts, and the like.

The polyoxyethylene sorbitan fatty acid esters include polyoxyethylenesorbitan mono coconut fatty acid ester, polyoxyethylene sorbitanmonolaurate, polyoxyethylene sorbitan monopalmitate, polyoxyethylenesorbitan monostearate, polyoxyethylene sorbitan tristearate. Thepolyoxyethylene sorbitol fatty acid esters include tetraoleatepolyoxyethylene sorbit.

In addition, the following substances can provide the effect similar tothat obtained by the above described dispersants.

Alkyl sulfate ester salts (for example, sodium lauryl sulfate, ammoniumlauryl sulfate, triethanolamine lauryl sulfate) and higher alcoholsulfuric ester salts such as higher alcohol sulfuric ester sodium salt,and polyoxyethylene alkylether sulfuric ester salts (for example, sodiumpolyoxyethylene laurylether sulfate, triethanolamine polyoxyethylenealkylether sulfate) can also be employed. Polyoxyethylene alkylethers(for example, polyoxyethylene laurylether, polyoxyethylene cetylether,polyoxyethylene stearylether), polyoxyethylene alkenylethers such aspolyoxyethylene oleylether, and polyoxyethylene higher alcohol etherscan be employed. Polyoxyethylene alkylphenylethers (for example,polyoxyethylene octylphenylether, polyoxyethylene nonylphenylether),polyoxyethylene alkylenephenylehter, and polyoxyethylene derivatives canbe employed. In addition, polyoxyethylene alkylamines, alkyl alkanolamides, alkylamine salts (for example, coconut amine acetate, stearylamine acetate), amine oxides such as lauryl dimethyl amine oxide, alkylbetaine or its analogues (for example, lauryl betaine, stearyl betaine,2-alkyl-N-carboxymethyl-H-hydroxyethyl imidazolinium betaine) can beemployed.

Among the above described dispersants of the present invention, it isparticularly preferable to use sodium; hexametaphosphate and sodiumpyrophosphate, and these compounds improves dispersibility of abrasivegrains in a dispersion medium to enable effective improvement ofpolishing efficiency.

The polishing material of the present invention may contain the abovedescribed anti-solidification agents and dispersants in any combination.It is the most effective to contain crystalline cellulose as ananti-solidification agent and sodium hexametaphosphate as a dispersantin combination in a polishing material, and the present inventors haveconfirmed that the combination is excellent as a polishing materialespecially for glass materials.

In addition, the polishing material in the present invention ispreferably such that each of the above described anti-solidificationagent and dispersant is contained at 0.02 to 2.0% by weight. When thecontent of each of the anti-solidification agent and dispersant is lessthan 0.02% by weight, it is impossible to soften abrasive grainprecipitates, the dispersibility of the abrasive grains in a dispersionmedium is deteriorated as well, and the efficiency of polishing isdecreased. On the other hand, an anti-solidification agent above 2.0% byweight allows softening abrasive grain precipitates, but tends to reducethe efficiency of polishing, while a dispersant above 2.0% by weightresults in a better dispersibility of the abrasive grains, but tends toharden abrasive grain precipitates.

That is, by containing each of the anti-solidification agent anddispersant at percentages of 0.02 to 2.0% by weight, both additives worktogether efficiently, so that high efficiency of polishing can beachieved.

In the polishing material having, as the major component, rare earthoxides including cerium oxide according to the present invention, thereis no limitation, particularly on the content of cerium oxide in thepolishing material. It is not preferable if the ratio of cerium oxide(CeO₂)/total rare earth oxides (TREO) exceeds 99%, because expensive andhigh-purity materials are required for raw materials, and the resultingpolishing material will be expensive as well. On the other hand, atratios of cerium oxide (CeO₂)/total rare earth oxides (TREO) less than40%, it is not preferable, since polishing values are reduced to a greatextent. Therefore, it is desirable that the ratio of cerium oxide (CeO₂)to the total rare earth oxides (TREO) in a polishing material is 40 to99%.

The above described polishing material according to the presentinvention can be dispersed into a water-born dispersion medium and usedas an abrasive slurry, but the method to produce the abrasive slurry ofthe present invention is not particularly limited. In other words, theabrasive slurry of the present invention may be prepared by preparingabrasive powder and powder containing an anti-solidification agent and adispersant separately in advance, mixing the powders, and then dispersedinto a water-born dispersion medium such, as water or a mixture of waterand water-soluble organic solvent. In this case, it is preferable tomill an anti-solidification agent and a dispersant into a size similarto that of an abrasive powder grain so as to proceed mixing of thepowders sufficiently. The abrasive slurry of the present invention canalso be prepared by charging an anti-solidification agent and adispersant directly into an abrasive slurry in a process of producing anabrasive before making abrasive powder, drying to obtain abrasive powdercontaining the anti-solidification agent and the dispersant, anddispersing the abrasive powder in a water-born dispersion medium.

In addition, the abrasive slurry of the present invention can be alsoprepared by charging an anti-solidification agent and a dispersant in awater-born dispersion medium such as water or a mixture of water andwater-soluble organic solvent to prepare an additive solution and addingabrasive powder to the additive solution. Further, the abrasive slurryof the present invention can also be prepared by dispersing abrasivepowder in a water-born dispersion medium in advance, then charging ananti-solidification agent and a dispersant in the dispersion, orsimultaneously charging abrasive powder, an anti-solidification agent,and a dispersant in a water-born dispersion medium. As described above,the order of mixing abrasive powder or slurry abrasive, ananti-solidification agent, and a dispersant or technique therefor is notparticularly restricted in preparation of the abrasive slurry of thepresent invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be explained below.

As a polishing material in the present invention was used onemanufactured by the following procedures. First, 20 kg of a concentratebastnaesite having 70% of TREO and 50% of CeO₂/TREO, and 20 l of purewater were milled for 5 hours in a wet-typed ball mill (a volume of 50l) with 120 kg of steel balls having a diameter of 5 mm, and thismilling process was carried out for 10 batches to prepare a large amountof powder slurry. The powder of this powder slurry had an average graindiameter of 0.9 μm. A cerium oxide-based polishing material wasmanufactured by treating the powder with hydrochloric acid having aconcentration of 1 mol/l and washing with pure water, followed byfiltration to obtain a cake, which in turn was dried and then roasted ina stationary furnace at 950° C. for 5 hours, followed by re-milling andclassifying. The cerium oxide-based polishing material obtained in thisway had a cerium oxide (CeO₂)/total rare earth oxides (TREO) of 50%.

First Embodiment: This first embodiment is directed to cases where inthe cerium oxide-based polishing material obtained as described above,the anti-solidification agent utilizes crystalline cellulose, and thedispersant utilizes sodium hexametaphosphate. In these cases, thedispersion medium in making a polishing slurry uses pure water, andcrystalline cellulose that is an anti-solidification agent uses oneunder the trade name of “Avicel” (manufactured by Asahi ChemicalIndustry, Co., Ltd.).

At first, three polishing materials were manufactured; one in which noadditive was added to the manufactured cerium oxide-based polishingmaterial (Comparative Example 1), one in which only ananti-solidification agent was added (Comparative Example 2), and one inwhich only a dispersant was added (Comparative Example 3), to carry outtheir characteristic evaluation, whose results are explained as follows.With respect to the characteristic evaluation, abrasive slurries ofComparative Examples 1 to 3 were prepared, and the polishing test,hardness test of settled cakes, and washing test were carried out toexamine their characteristics. For Comparative Examples 2 and 3,abrasive slurries were manufactured, varying the content of theanti-solidification agent or dispersant in the polishing material at 0.1wt %, 1.0 wt %, 2.0 wt %, to carry out their evaluation. Abrasiveslurries were made and used by adjusting the concentration of thepolishing material in a polishing slurry employed for the characteristicevaluation to be at 5 wt % in each evaluation (hereinafter, all thepolishing slurries in this embodiment were used by adjusting theconcentration of the polishing material to be at 5 wt %).

Table 1 shows the results of the polishing test when ComparativeExamples 1 to 3 were used. The polishing test was carried out using anOscar-typed polishing test machine (a model HSP-2I manufactured by TaitoSeiki Co., Ltd.)., Regarding polishing conditions, blue sheet glass waspolished as a substrate to be polished, employing a felt polishing pad.Polishing was performed for 10 minutes under the polishing conditionwhere an abrasive slurry was supplied at a rate of 25 ml/min., thepressure on the polished surface was set at 5.9 kPa(0.06 kg/cm ²), andthe rotation speed of the polishing machine was 500 rpm.

The characteristic evaluation in the polishing test was made bymeasuring a decrease in the weight of the blue sheet glass that is asubstrate to be polished, and calculating polishing values. Thepolishing values are values calculated by conversing, as relativevalues, weight decreases with the polishing materials of ComparativeExamples 2 and 3, using as the reference the weight decrease when theblue sheet glass was polished with the polishing material of ComparativeExample 1 under the above described condition (the weight decrease ofComparative Example 1 was defined as 100). Therefore, the polishingvalue is an index indicating that the higher the polishing value isrelative to 100, the better the efficiency of polishing is.

TABLE 1 Polishing Value (Relative Evaluation) Content 0 0.1 wt % 1.0 wt% 2.0 wt % Comparative No additive 100 Example 1 Comparative Crystalline91 81 79 Example 2 cellulose Comparative Sodium 103 111 112 Example 3hexameta- phosphate

As understood from Table 1, in case of containing only crystallinecellulose that is an anti-solidification agent, it is obviouslyindicated that there is a tendency to reduce the efficiency ofpolishing, as compared with Comparative Example 1 having no addedadditive, and a decrease in the efficiency of polishing becomesremarkable with its increasing content. Incase of containing only sodiumhexametaphosphate that is a dispersant, on the other hand, there is atendency to improve the efficiency of polishing relative to ComparativeExample 1, and it has been observed that the efficiency of polishing isimproved with its increasing content.

Next, Table 2 shows the results obtained by carrying out thesettled-cake hardness test. The settled-cake hardness test is a test inwhich the hardness of a settled cake is examined by placing a polishingslurry into a given vessel, and forming a settled cake by allowing it tostand for 48 hours to precipitate the abrasive grains of a polishingmaterial. The hardness of a settled cake was examined in five-leveledevaluation values, as relatively compared with the hardness of each ofsettled cakes, using as the reference the hardness of a settled cake forComparative Example 1 having no added additive. Specifically, thehardness of a settled cake for Comparative Example 1 was defined as anevaluation value of 3, and the evaluation values are given in fivelevels, depending on whether a cake has an equivalent hardness, or issofter or harder, as described below Table 2.

TABLE 2 Settled Cake Hardness Content 0 0.1 wt % 1.0 wt % 2.0 wt %Comparative No additive 3 Example 1 Comparative Crystalline 3 2 1Example 2 cellulose Comparative Sodium 4 5 5 Example 3 hexameta-phosphate Evaluation values of the settled cake hardness: 1: softer, 2:slightly softer, 3: equivalent, 4: slightly harder, 5: harder.

AS understood from Table 2, Comparative Example 2 clearly displays atendency for settled cakes to become soft as the content of crystallinecellulose is increased. In case of containing only sodiumhexametaphosphate, on the other hand, settled cakes are shown to have atendency to become very hard.

The following Table 3 shows the results of the washing test. The washingtest was carried out by visual observation of stains on the polishedsurface after carrying out 10 minute polishing under the above describedpolishing condition, and then immersing the blue sheet glass that is asubstrate to be polished, in pure water for 10 minutes, followed bysubjecting the glass to water-wash treatment by getting it three timesinto and out of pure water, and then drying. In the evaluation in thewashing test, relative comparison of washing test results for each ofthe polishing materials was made, using as the reference the washingresult for comparative Example 1 having no added additive, to examineits washing property, as in the above described settled-cake hardnesstest. Specifically, as described below Table 3, the washing result forcomparative Example 1 was defined as an evaluation value of 4, andevaluation values are given in six levels, depending on whether a resultis equivalent, or better or worse.

TABLE 3 Washing Properties Content 0 0.1 wt % 1.0 wt % 2.0 wt %Comparative No additive 4 Example 1 Comparative Crystalline 3 2 2Example 2 cellulose Comparative Sodium 4 4 4 Example 3 hexameta-phosphate Evaluation values in the washing test 1: little or no stain,2: better, 3: slightly better, 4: equivalent, 5: slightly worse, 6:worse.

As shown in Table 3, in case of containing only crystalline cellulose,there is a tendency for the washing property to become better, ascompared with Comparative Example 1, and it has turned out that thewashing property can be clearly improved, as the content of crystallinecellulose increases. In case of containing only sodiumhexametaphosphate, Comparative Example 3, on the other hand, littleimprovement in the washing property has been observed.

The following gives an explanation of Examples of the first embodiment.For these Examples, polishing materials were made, varying the contentof each of crystalline cellulose and sodium hexametaphosphate, and theabove described polishing test, settled-cake hardness test, washingtest, and settling test were carried out.

Results of these Examples are shown in Table 4, where the contents ofcrystalline cellulose and sodium hexametaphosphate are indicated incolumns and rows, respectively, and respective results obtained bycarrying out the polishing test, settled-cake hardness test, washingtest, and settling test are shown for polishing materials at eachcontent. The polishing values, and the evaluation values for the settledcake hardness and washing property in Table 4 are expressed by valuesdetermined by relative evaluation using as the reference the results forComparative Example 1 in which no additive was added, as in ComparativeExamples described above.

The settling test was performed to examine settling property by mixing110 g of each of polishing materials and 2090 g of pure water andstirring them thoroughly to prepare a polishing slurry containing 5 wt %of a polishing material, putting this polishing slurry into a 2000 mlmeasuring cylinder, and reading a gradation at the interface between thesuspension phase and the dispersion medium phase (pure water) in theabrasive slurry. The evaluation values of the settling test are valuesobtained by measuring the volume of the suspension phase after puttingthe polishing slurry into a measuring cylinder and allowing it to standfor 60 minutes, and calculating a ratio (%) of the measuredsuspension-phase volume relative to the whole polishing-slurry volume(2000 ml).

TABLE 4 Added Crystalline Cellulose (wt %) Amount 0 0.02 0.1 0.5 1.0 2.03.0 Sodium 0 A 100  96 91 85 81 79 77 Hexa- B  3  3  3  2  2  1  1 meta-C  4  4  3  3  2  2  1 phos- D 26 38 52 65 64 55 42 phate 0.02 A 102 101  100  123  115  98 79 (wt %) B  3  3  3  2  2  1  1 C  4  4  3  3  2 2  2 D 63 91 96 98 97 90 63 0.1 A 103  102  102  135  122  100  78 B  4 3  3  2  2  1  1 C  4  4  4  4  3  2  2 D 75 93 98 99 97 91 72 0.5 A107  105  104  137  125  102  79 B  4  3  3  3  2  2  1 C  4  4  4  4  3 2  2 D 88 96 99 100  99 92 75 1.0 A 111  108  106  140  127  104  80 B 5  3  3  3  3  2  2 C  4  4  4  4  3  2  2 D 89 97 98 99 97 91 70 2.0 A112  110  110  146  132  109  84 B  5  3  3  3  3  3  3 C  4  4  4  4  4 3  2 D 85 95 96 97 96 90 67 3.0 A 113  113  115  151  137  112  87 B  5 4  4  4  4  4  3 C  5  5  5  4  4  3  3 D 72 77 80 85 79 70 62 Row A:polishing values, Row B: settled cake hardness, Row C: washing property,Row D: ratios (%) of the suspension-phase volume at a period of 60minutes after making a polishing slurry.

As understood from Table 4, in the case where sodium hexametaphosphatehas a content more than 2.0 wt %, although the efficiency of polishingwill be improved, there is a tendency to diminish characteristics withrespect to the settled cake hardness and washing property. Whencrystalline cellulose has a content more than 2.0 wt %, on the otherhand, the settled cake hardness and washing property will become better,while it has turned out that there is a tendency to reduce theefficiency of polishing. From the results of the settling test indicatedin Row D, when the content of sodium hexametaphosphate is 0 wt % or 3.0wt %, it has been found that the ratio of the suspension-phase volume isdecreased, that is, sedimentation tends to occur. Based on these resultsof the settling test, it has turned out that the content range of sodiumhexametaphosphate resulting in a good dispersibility of the abrasivegrains of a polishing material in a polishing slurry is 0.02 to 2.0 wt%.

Then, with respect to all the properties of the efficiency of polishing,settled cake hardness, washing property, and dispersibility in thesettling test, the inventors examined the content range displaying goodproperties that are equivalent to or superior to those of ComparativeExample 1 having no additive. The content range in which all therespective properties were equivalent or superior, relative to those ofComparative Example 1 in this Table 4 (data of the upper-left corner inTable 4) is the region surrounded by the thick-line frame in Table 4.That is, it has turned out that if crystalline cellulose is contained inthe range of 0.02 to 2.0 wt % and sodium hexametaphosphate in the rangeof 0.02 to 2.0 wt %, totally balanced properties can be achievedconcerning the efficiency of polishing, settled cake hardness, washingproperty, and dispersibility in the settled test. In other words, thecerium oxide-based polishing material containing crystalline celluloseand sodium hexametaphosphate in contents within the content range isexcellent as a polishing material.

Next, an explanation is given regarding results of the examination ofchanges over time in the settling test and polishing test for polishingmaterials which contain 0.5 wt % of crystalline cellulose and 0.1 wt %of sodium hexametaphosphate. For comparison, a polishing material ofComparative Example 1 having no added additive was also examined.

The examination of changes over time in the settling test was carriedout by, after placing each of abrasive slurries in a measuring cylinderunder the condition in the above described settling test, subjecting itto the condition which leaves standing, measuring the volume of thesuspension phase at each period of 3, 15, 30, 45, and 60 minutes afterpouring, and calculating its ratio relative to the totalpolishing-slurry volume. Table 5 shows ratios (%) of thesuspension-phase volume at the time of each measurement.

TABLE 5 Settling Time (min.) 3 15 30 45 60 Comparative Example 1 83 4432 29 26 (no additive) 0.5 wt % crystalline 100 100 100 100 99cellulose + 0.1 wt % sodium hexametaphosphate (%)

As shown in Table 5, in Comparative Example 1 in which no additive wasadded, it has turned out that as the settling time is increased, thevolume of the suspension phase is correspondingly reduced, and earlierprecipitation takes place. That is, it has been proved that in polishingmaterials having no added additive, when polishing operations arecarried out continuously, aggregation between abrasive grains is caused,resulting in the precipitation of a polishing slurry, so that a decreasein the efficiency of polishing is brought about. In a polishing materialin which 0.5 wt % of crystalline cellulose and 0.1 wt % of sodiumhexametaphosphate were added, on the other hand, it was observed thatthe state where the ratio of the suspension-phase volume was 100% wasmaintained after it was poured, and even after a lapse of 20 minutes,the state was kept where the abrasive grains of a polishing materialwere well dispersed in a polishing slurry, and their precipitationproceeded very slowly.

Table 6 shows the results of the examination of changes over time in thepolishing test. The changes over time were examined by determining anamount decreased in the weight by means of polishing five successiveplates of blue sheet glass which were weighed before polishing under thesame condition as those of the above described polishing test, andmeasuring the weight of each plate of blue sheet glass after polishing.In Table 6, the efficiency of polishing is expressed by values to which,when the amount decreased in the weight of the first plate of blue sheetglass with Comparative Example 1 is defined as 100, amounts decreased inthe weight of the other plates are converted as relative values.Accordingly, values exceeding 100 in Table 5 indicate that amountsdecreased of the blue sheet glass by polishing are greater than that ofthe first plate of Comparative Example 1, and the efficiency ofpolishing is high.

TABLE 6 Plate Number 1 2 3 4 5 No Additive 100 93 90 86 84 0.5 wt %crystalline 135 136 135 134 135 cellulose + 0.1 wt % sodiumhexametaphosphate

As shown in Table 6, a polishing material of Comparative Example 1having no additive added has a tendency to reduce the efficiency ofpolishing over time, as the number of processed plates of blue sheetglass is increased. In a polishing material which contains 0.5 wt % ofcrystalline cellulose and 0.1 wt % of sodium hexametaphosphate, on theother hand, it has turned out that even if the number of processedplates of blue sheet glass is increased, there is hardly any change inthe efficiency of polishing, and thus a high efficiency of polishing canbe achieved stably.

Then, the results of evaluation conducted after changing the method ofproducing the abrasive slurries will be explained. The abrasive slurriesused in Tables 1 to 6 described above were prepared by mixing abrasivepowder with an anti-solidification agent and a dispersant in advance,then disperse the mixture into pure water to make slurry. The abrasiveslurries evaluated here were prepared by disperse abrasive powdercontaining no anti-solidification agent or dispersant into pure water tomake a slurry in advance, and then adding crystalline cellulose andsodium hexametaphosphate to the slurry. For the respective evaluations,the polishing test, settled-cake hardness test, washing test, andsettling test were carried out as in Table 4. As Evaluation Item E, theresults of measurement of the settled-cake height 30 days later by thesettling test for Evaluation Item Dare also shown. For Evaluation E, theresults are expressed in a relative value calculated based on the heightof the settled cake containing no crystalline cellulose or sodiumhexametaphosphate (0 wt % in Table 7) 30 days later assuming as 100. Theresults of evaluations shown here are obtained only for the case wherecrystalline cellulose and sodium hexametaphosphate were added in thesame amount. The results are shown in Table 7.

TABLE 7 Content of crystalline cellulose or sodium hexametaphosphate (wt%) 0 00.2 0.1 0.5 1.0 2.0 3.0 A 99 100  103  135 130  107  85 B  3  3  3 3  3  3  3 C  4  4  4  4  3  3  3 D 29 92 98 100 96 92 59 E 100  360 410  430 440  420  210 

From a comparison between the results in Table 7 and those in Table 4,it was confirmed that the difference in procedure to prepare an abrasiveslurry did not largely affect the results of the polishing test,settled-cake hardness test, washing test, or settling test with respectto the polishing material shown in the first embodiment.

Second Embodiment: In this second embodiment, an explanation of caseswhere the anti-solidification agent utilized calcium secondaryphosphate, a condensate of sodium β-naphthalenesulphonate and formalin,and synthetic silica, and the dispersant utilized sodium pyrophosphatewill be given. In this second embodiment, the calcium secondaryphosphate used was a guaranteed reagent, the condensate of sodiumβ-naphthalenesulphonate and formalin used was a product under the tradename of “Lavelin” (manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.),and the synthetic silica used was a product under the trade name of“Carplex” (manufactured by Shionogi & Co., Ltd.).

In this second embodiment, the above described cerium oxide-basedpolishing materials were employed to make polishing materials containing1.0 wt % of each of anti-solidification agents and 0.5 wt % of sodiumhexametaphosphate as dispersant, and polishing materials containing 1.0wt % of crystalline cellulose that is an anti-solidification agent and0.5 wt % of sodium pyrophosphate that is a dispersant for carrying outthe polishing test, settled-cake hardness test, washing test, andsettling test. Results are shown in Table 8, where data, shown inExamples of the first embodiment, for a polishing material whichcontains 1.0 wt % crystalline cellulose and 0.5 wt % sodiumhexametaphosphate are included for comparison. Polishing values,evaluation values for the settled cake hardness and washing property,and the ratios of the suspension-phase volume shown in Table 6 are thosemeasured in a similar way to what is explained in the first embodiment.

TABLE 8 Anti-solidification Dispersant agent (1.0 wt %) (0.5 wt %)Crystalline Cellulose Sodium A 125 Hexametaphosphate B 2 C 3 D 99Crystalline Cellulose Sodium Pyrophosphate A 119 B 2 C 3 D 98 CalciumSecondary Sodium A 128 Phosphate Hexametaphosphate B 2 C 4 D 97 SodiumSodium A 118 β-Naphthalenesulphonate Hexametaphosphate B 2 FormalinCondensate C 3 D 98 Synthetic Silica Sodium A 127 Hexametaphosphate B 2C 4 D 99 Row A: polishing value (g), Row B: settled cake hardness, RowC: washing property, Row D: ratio of the suspension-phase volume at aperiod of 60 minutes after making a polishing slurry.

As shown in Table 8, it has turned out that polishing materials in caseof containing calcium secondary phosphate, a condensate of sodiumβ-naphthalenesulphonate and formalin, and synthetic silica asanti-solidification agent, and sodium hexametaphosphate as dispersanthave characteristic data that are almost equivalent to those ofpolishing materials containing the same amounts of crystalline celluloseand sodium hexametaphosphate. In addition, it has turned out thatpolishing materials containing crystalline cellulose and sodiumpyrophosphate also have characteristics at equivalent levels to those ofpolishing materials containing sodium hexametaphosphate as dispersant.

Third Embodiment: In the third embodiment, the results of evaluationconducted on the combinations of the anti-solidification agents and thedispersants shown in Table 9 will be described. Regarding evaluation,the polishing test, settled-cake hardness test, washing test, andsettling test conducted as in First and Second Embodiments wereconducted. The abrasive slurries used for the evaluation were producedin similarly manner to those used for Tables 1 to 6. The results areshown in Table 10.

TABLE 9 Anti-solidification agent Dispersant (0.3 wt %) (0.3 wt %) aPropylene glycol alginate Sodium polyacrylate b Propylene glycolalginate Sodium hexametaphosphate c Synthetic silica Sodium polyacrylated Colloidal silica Acrylic acid/maleic acid copolymer sodium salt eColloidal silica Sodium pyrophosphate f Crystalline cellulose Acrylicacid/maleic acid copolymer sodium salt g Sodium alginate Sodiumpolystyrene sulfonate h Sodium alginate Sodium hexametaphosphate *iCrystalline cellulose + Sodium polystyrene sulfonate Sodiumcarboxymethylcellulose j Fumed silica Polyoxyethylene sorbitan stearatek Fumed silica Sodium pyrophosphate l Sodium β-naphthalenePolyoxyethylene sorbitan stearate sulfonate formalin condensate mCrystalline cellulose + Tetraoleate polyoxyethylene sorbitcarboxymethylcellulose n Propylene glycol alginate Tetraoleatepolyoxyethylene sorbit *The weight ratio of crystalline cellulose tosodium carboxymethylcellulose is approximately 9 to 1.

TABLE 10 a b c d e f g A 120  119  122  121  123  122  120  B  3  3  3 3  3  2  2 C  4  4  4  4  4  4  4 D 96 95 97 95 96 97 95 h I j k l m NA 118  125  123  120  120  122  119  B  3  2  3  3  3  3  3 C  4  4  4 4  4  4  4 D 95 98 96 97 95 96 96

The polishing materials containing the anti-solidification agents anddispersants in 14 combinations from a to n shown in Table 9 wereevaluated. As a result, as shown in Table 10, it was found that thecharacteristics of the 14 polishing materials were similar to thecharacteristic data for the polishing material containing crystallinecellulose and sodium hexametaphosphate in the same amount in FirstEmbodiment.

INDUSTRIAL APPLICABILITY

According to the present invention, the dispersibility of the abrasivegrains of a polishing material can be made better and the hardness ofabrasive grain precipitates can be reduced, and at the same time a highefficiency of polishing can be achieved stably. That is, according tothe present invention, a polishing material with requiredcharacteristics of a polishing material with a totally very goodbalance, particularly extremely excellent as a polishing material isprovided.

What is claimed is:
 1. A polishing material comprising, as a majorcomponent, abrasive grains of cerium oxide and at least one other rareearth oxide, an anti-solidification agent selected from the groupconsisting of crystalline cellulose, calcium secondary phosphate, andsynthetic silica, and a dispersant selected from the group consisting ofsodium hexametaphosphate or sodium pyrophosphate, wherein the dispersantis present in an amount effective to disperse the abrasive grainscontained in the polishing material into a water-based dispersionmedium, and the anti-solidification agent is present in an amounteffective to soften the abrasive grains of the polishing material whensaid abrasive grains are dispersed into said dispersion medium.
 2. Thepolishing material according to claim 1, wherein the polishing materialcontains 0.02-2.0 weight % of the anti-solidification agent and 0.02-2.0weight % of the dispersant based on the total weight of the composition.3. The polishing material according to claim 1, wherein the cerium oxide(CeO₂) content is 40 to 99 weight % of the total rare earth oxide (TREO)content.
 4. An abrasive slurry comprising the polishing material ofclaim 1 dispersed into a water-based dispersion medium.